The present invention relates to a DC-to-DC converter and a converting method, and more particularly to a DC-to-DC converter and a converting method for adjusting a turn ratio of a transformer in order to maintain an output DC voltage during a hold-up time in response to a voltage drop of an input DC voltage.
Presently, the traditional topological structure of DC-to-DC converter is mainly divided into four types: full-bridge converter, forward converter, flyback converter and asymmetrical half-bridge converter.
FIG. 1 illustrates a circuit diagram of a conventional full-bridge topological DC-to-DC converter, wherein the power switching devices Q1 to Q4 are MOSFETs.
In view of FIG. 1, the DC-to-DC converter includes a direct current (DC) voltage Ud provided from the DC power supply or obtained from a rectified AC power supply, a filtering energy storage capacitor C1, a switch assembly Q1 to Q4, a transformer T1, two rectifying diodes D2 and D3 and a filtering circuit LC having a capacitor C3 and an inductor L2. The filtering energy storage capacitor C1 is charged by the DC voltage Ud provided from the DC power supply or obtained from a rectified alternating current (AC) power supply. The input DC voltage is converted into a high frequency AC voltage by alternately conducting and shutting the switch assembly Q1 to Q4. Furthermore, the high frequency AC voltage transformed by the transformer T1 is transferred to the secondary winding N2 and N2xe2x80x2 in the transformer T1, which are rectified through the rectifying diodes D2 and D3 respectively and then a DC output voltage is outputted from the filtering circuit LC.
During normal operation, the maximum duty ratio in the switch assembly Q1 to Q4 is generally small. The small duty ratio is obtained so as to conform to a hold-up time in a power supply. When the input DC outputted from the power supply is dropped, a voltage outputted from the filtering energy storage capacitor C1 is decreased therewith. Nevertheless, the power supply is required to maintain a hold-up time, e.g. 20 ms, of rated output voltage of the converter after the input voltage drop. Consequently, the duty ratio of the converter is raised through the hold-up time, for example the duty ratio is raised from 70% of working normally to 90%, thereby the limited output voltage of the converter is performed.
The duty ratio of the converter is less during the normal operation, and hence the efficiency of the converter could not be increased. Moreover, the converter needs a larger filtering energy storage capacitor C1 to maintain the rated output voltage, which increases the volume of the converter and the price thereof. In addition, voltage on the secondary winding of the transformer T1 should be raised due to the less duty ratio and the stress generated from the rectifying diodes D2 and D3 would be increased.
Furthermore, other topological structures of the DC-to-DC converter also exist the above-mentioned shortcomings according to the prior art. It is therefore tried by the applicant to deal with the above situation encountered by the prior art.
It is therefore an object of the present invention to provide a DC-to-DC converter and a method for keeping a rated output voltage by adjusting the turn ratio of a transformer when the input voltage outputted from a power supply is dropped.
It is another object of the present invention to provide a DC-to-DC converter and a method for converting direct current to direct current including a better converting efficiency by raising the duty ratio of a switch assembly during the normal operation.
According to an aspect of the present invention, the DC-to-DC converter includes a power supply, a first capacitor, a first switch assembly, a transformer, a rectifying circuit, a filtering circuit and a range winding assembly. The power supply is used for providing a first direct current (DC). The first capacitor is electrically connected to the power supply for being charged by the power supply. The first switch assembly is electrically connected to the first capacitor for converting the first direct current into a first alternating current by switching the first switch assembly. The transformer has a primary winding and a secondary winding for converting the first alternating current to a second alternating current, wherein the primary winding is electrically connected to the first switch assembly and the secondary winding has a tap. The rectifying circuit is electrically connected to the secondary winding for converting and rectifying the second alternating current to a second direct current. The filtering circuit is electrically connected to the rectifying circuit for filtering the second direct current. In addition, the range winding assembly is electrically connected to the secondary winding and is one portion of the secondary winding for adjusting the output voltage of the second direct current in response to the voltage drop of the first direct current.
Preferably, the power supply is a direct current (DC) power supply.
Preferably, the power supply is an alternating current (AC) power supply capable of providing the first direct current via rectifying.
Preferably, the first capacitor is a filtering capacitor.
Preferably, the first alternating current is a high frequency alternating current.
Preferably, the tap is a central tap.
Preferably, the rectifying circuit includes two first rectifying diodes electrically connected to two ends of the secondary winding, respectively.
Preferably, the filtering circuit includes an inductor and a second capacitor electrically connected to the tap.
Preferably, the range winding assembly includes two subwindings electrically connected with two ends of the secondary winding, respectively.
Preferably, the two subwindings are electrically connected with two second rectifying diodes, respectively, wherein the output ends of the two second rectifying diodes are connected together and electrically connected to the inductor of the filtering circuit.
Preferably, the DC-to-DC converter further includes a third rectifying diode electrically connected to the range winding assembly, and a second switch electrically connected between the third rectifying diode and the filtering circuit.
Preferably, the DC-to-DC converter further includes a control circuit electrically connected to the second switch for controlling the second switch in response to the voltage drop.
Preferably, the control circuit is electrically connected to the first capacitor for providing a control signal to switch the second switch in response to the voltage drop of the first capacitor when the first direct current outputted from the power supply is dropped.
Preferably, the control circuit is electrically connected to the secondary winding of the transformer for providing a control signal to switch the second switch in response to the voltage drop of the secondary winding when the first direct current outputted from the power supply is dropped.
Preferably, the DC-to-DC converter is one selected from a group consisting of a flyback converter, a forward converter and a half-bridge converter.
According to another aspect of the present invention, the DC-to-DC converter includes a power supply for providing a first direct current (DC), a first capacitor electrically connected to the power supply for being charged by the power supply, a first switch assembly electrically connected to the first capacitor for converting the first direct current into a first alternating current by switching the first switch assembly, a transformer having a primary winding electrically connected to the first switch assembly and a second winding for converting the first alternating current into a second alternating current, a rectifying circuit electrically connected to a first end of the secondary winding for converting and rectifying the second alternating current to a second direct current, a filtering circuit having an inductor and a second capacitor for filtering the second direct current, wherein the inductor is electrically connected to the rectifying circuit, and the second capacitor is electrically connected to a second end of the secondary winding, a subwinding electrically connected to the first end of the secondary winding, a second rectifying diodes electrically connected to the subwinding, wherein the output end of the subwinding is electrically connected to the inductor of the filtering circuit, a second switch electrically connected between the subwinding and the filtering circuit, and a control circuit electrically connected to the second switch for controlling the second switch to be turned on when the voltage of the first direct current is dropped.
Preferably, the control circuit is electrically connected to the first capacitor for providing a control signal to switch the second switch in response to the voltage drop of the first capacitor when first direct current outputted from the power supply is dropped.
Preferably, the DC-to-DC converter is one selected from a group consisting of a flyback converter, a forward converter and a half-bridge converter.
According to another aspect of the present invention, the DC-to-DC converter includes a power supply for providing a first direct current (DC), a first capacitor electrically connected to the power supply for being charged by the power supply, a first switch electrically connected to the first capacitor for converting the first direct current into a first alternating current by switching the first switch assembly, a transformer having a primary winding electrically connected to the first switch and a second winding for converting the first alternating current into a second alternating current, a rectifying circuit electrically connected to the second winding for converting and rectifying the second alternating current to a second direct current, a filtering circuit having an inductor and a second capacitor, and electrically connected to the rectifying circuit for filtering the second direct current, a second switch having one end electrically connected to a central tap of the primary winding and the other end electrically connected to the first capacitor, and a control circuit for controlling the first switch and the second switch in response to the voltage drop of the first direct current outputted from the power supply.
Preferably, the control circuit is electrically connected to the first capacitor for providing a control signal to switch the second switch in response to the voltage drop of the first capacitor when first direct current outputted from the power supply is dropped.
Preferably, the DC-to-DC converter is one selected from a group consisting of a flyback converter, a forward converter and a half-bridge converter.
According to another aspect of the present invention, there is provided a method for converting direct current to direct current, adapted to be applied in a DC-to-DC converter. The method includes steps of charging a first capacitor, switching a first switch assembly for converting a first direct current outputted from the first capacitor into a first alternating current, converting the first alternating current to a second alternating current via a transformer, detecting whether the voltage of the first direct current is dropped, and adjusting the ratio of the windings for changing the output voltage of the second alternating current in response to the voltage drop, rectifying and converting the second alternating current into a second direct current via a rectifying circuit, and filtering the second direct current via a filtering circuit.
Preferably, the detecting step is performed by detecting the voltage drop of the first capacitor.
Preferably, the detecting step is performed by detecting the voltage drop of a second winding of the transformer.
Preferably, the adjusting step is performed by increasing the number of a second winding of the transformer.
Preferably, the adjusting step is performed by reducing the number of a primary winding of the transformer.
Preferably, the DC-to-DC converter is one selected from a group consisting of a flyback converter, a forward converter and a half-bridge converter.
The present invention may be well understood through the following descriptions with reference to the accompanying drawings, in which: